At Military History Now, there’s a look at a few of the allied plans for invading France before the actual June 6, 1944 operation:

IKE’S SLEDGEHAMMER
Almost as soon as America entered the war with Nazi Germany, generals Dwight Eisenhower and George Marshall were both lobbying for a strike across the English Channel into France. One plan foresaw a joint British and American assault on either of the French port cities of Cherbourg or Brest as early as the fall of 1942. The operation, codenamed Sledgehammer, would see a force of just six divisions attack, capture and hold either one of the two strategically-vital, deep-water harbours. The force, which likely would have totalled no more than 60,000 men, would have been expected to withstand the inevitable Nazi counterattacks until spring when more reinforcements could arrive. Despite the fact that the Germans would have been free to throw as many as 30 divisions at the invaders, the U.S. Joint Chiefs (as well as the Soviets) endorsed Sledgehammer wholeheartedly. The American commanders seemed to favour any plan that would bring U.S. forces into action in Europe quickly, while Stalin was thrilled at the prospect of an Allied offensive in Western Europe — anything to divert German forces away from the Russian front. Oddly enough, while the mission called for the heavy use of American air and sea power, at the time there was still only a handful of combat-ready U.S. Army units in England. As such, the ground portion of the invasion would be left entirely up to the British military. Cooler heads, namely Prime Minister Churchill, convinced Eisenhower to shelve Sledgehammer – Britain was already stretched thin in Egypt and America still had yet to fully mobilize for the war in Europe. An invasion of France would simply have to wait.

OPERATION ROUNDUP
Later in 1942, the Allies roughed out a second plan to put troops ashore in Western Europe the following spring. This operation, dubbed Roundup, called for 18 British and 30 American divisions to hit a series of landing zones along a 200 km stretch of coastline between Boulogne-sur-Mer near Calais and the port of Le Harve. Overhead, more than 5,700 Allied aircraft were to sweep the skies of the Luftwaffe clearing the way for a series of airborne drops. D-Day was set for some time in April or May of 1943. The British, already strained by three years of total war against the Axis, were understandably reluctant to throw their army headlong into the teeth of Germany’s Channel fortifications. They pushed instead to attack Sicily and Italy – what Churchill called the “soft underbelly of Europe” — by way of North Africa. A sober appraisal of British and American fleet strength, air assets and manpower ultimately convinced the Allied high command that no invasion could be mounted until 1944 at the earliest. For one thing, American factories had yet to manufacture enough of the landing craft needed for such a massive undertaking. Washington and London turned their attention instead towards a late 1942 invasion of Tunisia – Operation Torch. The rest is, as they say, history.

As any Canadian military historian would probably have said to either of these proposals … I have two words: Operation Jubilee.

The Dieppe Raid, also known as the Battle of Dieppe, Operation Rutter and, later, Operation Jubilee, was a Second World War Allied attack on the German-occupied port of Dieppe. The raid took place on the northern coast of France on 19 August 1942. The assault began at 5:00 a.m. and by 10:50 a.m. the Allied commanders were forced to call a retreat. Over 6,000 infantrymen, predominantly Canadian, were supported by a Canadian Armoured regiment and a strong force of Royal Navy and smaller Royal Air Force landing contingents.

The objective of the raid was discussed by Winston Churchill in his war memoirs:

“I thought it most important that a large-scale operation should take place this summer, and military opinion seemed unanimous that until an operation on that scale was undertaken, no responsible general would take the responsibility of planning the main invasion…

In discussion with Admiral Mountbatten it became clear that time did not permit a new large-scale operation to be mounted during the summer (after Rutter had been cancelled), but that Dieppe could be remounted (with the new code-name “Jubilee”) within a month, provided extraordinary steps were taken to ensure secrecy. For this reason no records were kept but, after the Canadian authorities and the Chiefs of Staff had given their approval, I personally went through the plans with the C.I.G.S., Admiral Mountbatten, and the Naval Force Commander, Captain J. Hughes-Hallett.”

Objectives included seizing and holding a major port for a short period, both to prove it was possible and to gather intelligence from prisoners and captured materials, including naval intelligence in a hotel in town and a radar installation on the cliffs above it. Although the primary objective was not met and secondary successes were relatively few, some knowledge was gained while assessing the German responses. The Allies also wanted to destroy coastal defences, port structures and all strategic buildings. Due to the failure to secure Dieppe this objective was not met in any systematic sense. The raid had the added objective of providing a morale boost to the troops, Resistance, and general public, while assuring the Soviet Union of the commitment of the United Kingdom and the United States.

A total of 3,623 of the 6,086 men (almost 60%) who made it ashore were either killed, wounded, or captured. The Royal Air Force failed to lure the Luftwaffe into open battle, and lost 96 aircraft (at least 32 to flak or accidents), compared to 48 lost by the Luftwaffe.[2] The Royal Navy lost 33 landing craft and one destroyer. The events at Dieppe later influenced preparations for the North African (Operation Torch) and Normandy landings (Operation Overlord).

Operation Jubilee clearly showed that the plans for both Sledgehammer and Roundup would have been bloody failures.